fix typescript errors

[pmcelhaney]

• minor type fix in response-builder-factory.ts
• revert change in use substring for content type parsing #1372 which broke type shortcuts like .json(), .html(), etc.

[changeset-bot]

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Latest commit: 89acaa1

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[coveralls]

Pull Request Test Coverage Report for Build 20965838127

Details

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 84.26%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/server/types.ts	0	2	0.0%

Totals
Change from base Build 20864959310:	0.0%
Covered Lines:	3562
Relevant Lines:	4313

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💛 - Coveralls